Cube (formerly Cube.js) is a universal semantic layer and agentic analytics platform — it sits between your data sources and every consumer of them, enforcing consistent metric definitions through engineer-authored data models, and caching results for sub-second performance. PlyDB takes a different approach: agents connect to live sources directly and build semantic context themselves through OSI overlays that accumulate across sessions. Both are Apache 2.0 open source and both ship native MCP servers. The core difference is the semantic model: engineer-defined and enforced upfront in Cube, or agent-built and compounding over time in PlyDB.
| Cube | PlyDB | |
|---|---|---|
| Semantic model approach | Engineer-authored YAML/JS — measures, dimensions, and joins defined upfront and enforced consistently across all consumers | Agent-authored OSI overlays — schema auto-discovered; agents accumulate business context across sessions that informs future queries |
| Pre-aggregation & query caching | Built-in relational caching engine — automatically builds condensed datasets for sub-second analytics at scale | No caching layer — queries execute live against source databases |
| Multi-protocol APIs | REST, GraphQL, SQL (Postgres wire protocol), MDX, and MCP — one semantic layer, any consumer | MCP and CLI — purpose-built for AI agent access |
| Built-in AI agents | AI Data Analyst and AI Data Engineer agents — natural language analytics and automated model authoring via Cube Agentic Analytics | Not applicable — PlyDB is the data layer; AI reasoning lives in your external agent |
| Agent integration (MCP) | Native MCP server — Premium and Enterprise plans only; exposes the semantic layer to MCP-compatible agents | Native MCP & CLI — available in the open-source binary, no paid plan required |
| Time to first query | Requires cube model authoring before agents or BI tools can query — hours to days depending on data complexity | Minutes — auto-discovers schema; agents start querying immediately and build context over time |
| Live operational DB access | Queries go through the semantic model; pre-aggregations add a refresh cycle between source changes and query results | Direct — agents query live data with no caching cycle in between |
| Cross-source queries | Supported via rollup joins across configured data sources — aggregated level, not arbitrary row-level JOINs | Arbitrary SQL JOIN across any connected source in one query |
| Semantic context for agents | Engineer-defined measures and dimensions surface to agents via the API — consistent, governed, requires upfront authoring | OSI overlays — agents auto-discover schema and write context that persists and compounds across sessions; advisory but substantive |
| Deployment complexity | Cube Core requires Kubernetes for production; Cube Cloud is fully managed SaaS | Single binary, one JSON config file — runs anywhere without cluster infrastructure |
| Open source | Apache 2.0 (Cube Core); Cube Cloud is proprietary SaaS | Apache 2.0 |
| Cost | Cube Core: free; Cube Cloud: free tier (1K queries/day), CCU-based paid plans; MCP on Premium+ | Open source — Apache 2.0 |
Cube is an open-source universal semantic layer that sits between your data sources and every consumer of them — BI tools, AI agents, embedded analytics, and custom applications. Data engineers define cubes, dimensions, measures, and joins in YAML or JavaScript; Cube enforces these definitions consistently across its REST, GraphQL, SQL (Postgres wire protocol), MDX, and MCP APIs. Its built-in relational caching engine materializes pre-aggregations for sub-second query performance at high concurrency. Cube Agentic Analytics (GA October 2025) adds AI Data Analyst and AI Data Engineer agents powered by Claude or a bring-your-own LLM. Cube Core is Apache 2.0; the MCP server requires a Cube Cloud Premium or Enterprise plan.
PlyDB is an open-source gateway built from the ground up for AI agents. You declare your data sources in a single JSON config file — PostgreSQL, MySQL, SQLite, S3, files, Google Sheets — and any AI agent connects immediately via native MCP or CLI, with no data modeling required before the first query. PlyDB's semantic context system auto-discovers schema and provides an OSI-format overlay system where agents record institutional knowledge — enum meanings, business rules, domain context — that persists and compounds across sessions. Read-only by design, single binary, and the MCP server ships with the open-source release at no additional cost.
These tools can complement each other. Teams running Cube for governed BI and multi-consumer analytics can deploy PlyDB alongside it as the agent gateway to operational databases and ad-hoc sources that don't belong in a cube model — sources that still need to be reachable by agents without going through a modeling phase first.
Auto-discover schema. OSI overlays that compound across sessions. MCP included. Open source.
Apache License 2.0